JPH10310823A - Manufacture of shaft-shaped parts for machine structural use, excellent in fatigue characteristic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide shaft-shaped parts for machine structural use, having a hole perpendicular to axial direction and excellent in fatigue characteristic. SOLUTION: The shaft-shaped parts for machine structural use are manufactured by using a steel for induction hardening, having a composition containing, by weight, 0.25-0.55% C, <=0.30% Si, 0.20-1.50% Mn, 0.05-1.30% Cr, and 0.01-0.06% Al. At this time, induction hardening is performed so that the hardened layer ratio in the hole part perpendicular to axial direction satisfies t/R>=0.5 in the case of a solid article or satisfies t/T>=0.5 in the case of a hollow article, where (t) is hardening depth to 50% martensite hardness and also R and T are parts radius and inside thickness, respectively. Further, the horizontal hole part is subjected to shot peening treatment of 0.5-1.2 mmA arc height by the use of a projection material of 0.5-1.5m m grain size and 600-850 HV hardness and then to shot peening treatment of 0.15-0. 50 mmA arc height by the use of a projection material of 0.03-0.5 mm grain size and 600-850 HV hardness, or, respective shot peening treatments are applied independently.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shaft which is a shaft-shaped part made of steel for machine structural use, and more particularly to a shaft-shaped part having a hole perpendicular to the axial direction and having excellent fatigue characteristics. The present invention relates to a method for manufacturing a component for use.

[0002]

2. Description of the Related Art In general, shafts and the like, which are shaft-shaped parts for machine structures, are required to have excellent fatigue strength. Therefore, a predetermined shape is formed by hot forging, cold forging, rolling, cutting, or the like. After production, surface hardening treatment such as carburizing and induction hardening is often performed. In particular, induction quenching has attracted attention as a useful strengthening method for mechanical structural parts because it has the advantages of low processing cost and short processing time, and has little quenching distortion and a clean surface.

[0003] In recent years, it has been desired to reduce the weight of automobiles and the like for the purpose of reducing fuel consumption and exhaust gas, and to increase the strength of mechanical structural parts accompanying the increase in engine output. In response to such a need for high strength, a method of increasing the depth of the hardened layer until a 50% martensite hardness is obtained is taken as a means for improving the fatigue strength of a mechanical structure component subjected to induction hardening. ing. In the case of carbon steel used as conventional parts for mechanical structures, it is necessary to increase the induction quenching heating time as a method of increasing the depth of the hardened layer. There is a problem that the fatigue strength is reduced due to a decrease in residual stress and a decrease in surface hardness. Therefore, the hardenability can be increased by adding the alloy element, and the depth of the hardened layer can be increased, thereby improving the fatigue strength. However, at present, even if the hardened layer ratio t / R (t: hardened layer depth up to 50% martensite hardness, R: component radius) exceeds 0.5 and the quenching depth is increased, the fatigue strength does not increase. Saturates,
It is at the upper limit of high strength.

In particular, in the case of a shaft-shaped component having a lateral hole perpendicular to the axial direction, the starting point of fatigue failure is the lateral hole, and the compressive residual stress generated during induction hardening is lower than that of a component having no lateral hole.
Even if the depth of the hardened layer is increased, the improvement in the fatigue strength is slight. Further, in the range of the hardened layer ratio of 0.5 or more, even if the hardened layer depth is increased, the fatigue strength tends to decrease. To date, to meet the need for higher strength shaft parts,
JP-A-4-141521 and JP-A-7-9037
No. 9 proposes a method for producing a shaft-like component having excellent torsional strength by subjecting a steel material to induction hardening and then performing shot peening. However, the method described in the above publication is not sufficient for the need for increasing the strength of a shaft-shaped component having a lateral hole, and it is desired to realize a shaft-shaped component capable of obtaining higher torsional fatigue strength. .

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a component for a mechanical structure having excellent fatigue characteristics in a shaft-shaped component having a lateral hole and a method of manufacturing the same, focusing on the above-mentioned conventional problems.

[0006]

According to the present invention, there is provided a machine structural component and a method of manufacturing the same, wherein C: 0.25
0.55%, Si: 0.30% or less, Mn: 0.20%
1.50%, Cr: 0.05 to 1.30%, Al: 0.
01-0.06%, desirably B: 0.0005-0.
0035%, N: 0.015% or less, Ti: 0.01 to
It is regulated to 0.05%, contains one or two kinds of Mo: 0.5% or less and Ni: 1.0% as needed, and further improves the machinability as needed. : 0.01 ~
0.10%, Pb: 0.01 to 0.20%, Bi: 0.
01 to 0.30%, Te: 0.005 to 0.10%, C
a: When manufacturing a shaft-shaped component for a machine structure having a horizontal hole perpendicular to the axial direction by using induction hardening steel containing one or more of 0.0003 to 0.010%, a horizontal hole portion In the case of a solid product having a hardened layer ratio of t / R = 0.5 or more (t:
In the case of a hardened layer depth up to 50% martensite hardness, R: component radius) or a hollow product, t / T = 0.5 or more (T:
Thickness) and induction hardening, and a grain size of 0.
After a shot peening process with an arc height of 0.5 to 1.2 mmA using a projection material having a hardness of 5 to 1.5 mm and a hardness of 600 to 850 HV, a projection having a particle size of 0.03 to 0.5 mm and a hardness of 600 to 850 HV is performed. Arc height 0.15
It is characterized in that a shot peening process of 0.50 mmA is performed or a shot peening process is performed independently.

[0007]

The induction hardening steel used as a raw material in the method of manufacturing a component for a machine structure according to the present invention is added with an alloy element for increasing hardenability so as to ensure a sufficient induction hardening depth. The alloy elements are adjusted to improve the fatigue crack propagation characteristics of the induction hardened part. Further, the fatigue strength is greatly improved by increasing the induction hardening depth, shifting the fracture origin to the vicinity of the shaft surface, performing shot peening treatment, and effectively applying residual stress. Hereinafter, the reasons for the limitation of the component range, the hardened layer depth, and the shot peening treatment conditions of the steel for induction hardening used as a raw material in the method for producing a machine structural component according to the present invention will be described.

C: 0.25 to 0.55% C is an element necessary for securing the strength of the parts for machine structural use. In particular, in order to obtain sufficient surface hardness by induction hardening, C is 0.25%. The above content is required. However, if the content exceeds 0.55%, quenching cracks are likely to occur during induction hardening, so the content is limited to 0.55% or less.

Si: 0.30% or less Si is an element that is contained as a deoxidizing agent at the time of melting and improves the hardenability. However, if added in a large amount exceeding 0.30% or more, cracks are likely to occur during hot working, so the content is limited to 0.30% or less.

Mn: 0.20 to 1.50% Mn is an element that acts as a desulfurizing agent at the time of melting and is an element that improves hardenability. 0.20% for improving induction hardenability of steel and increasing surface hardness
It is necessary to add above. However, even when added in a large amount exceeding 1.5%, the quenchability is saturated, and the content is limited to 1.5% or less to reduce the hot workability.

Cr: 0.05 to 1.30% Cr is an element which is effective for improving the quenchability of Mn and for obtaining a sufficient quench depth by induction hardening.
For that purpose, it is necessary to add 0.05% or more. However, even if it is added in a large amount exceeding 1.30%, the hardenability is saturated, and the cold workability is deteriorated. Therefore, even if it is added, it is limited to 1.30% or less.

Al: 0.01 to 0.06% Al is an element necessary for deoxidation, but it prevents coarsening of crystal grains during induction hardening, improves strength, and reduces strain after induction hardening. It is an element effective for remarkably reducing the size. To obtain such an effect, the content is 0.01% or more. However, if added over 0.06%,
Since the toughness of steel is reduced, the content is limited to 0.06% or less.

B: 0.0005-0.0035% B is added to secure a necessary induction hardening depth.
Further, it is an element that improves the grain boundary strength, and it is necessary to contain 0.0005% or more in order to obtain such an effect. However, the effect saturates as the amount increases, and the adverse effect of reducing hot workability appears.
0.0035% or less.

N: 0.015% or less If the N content is too large, the deformation resistance increases and the cold workability decreases, so it is desirable to limit the content to 0.015% or less.

Ti: 0.01% to 0.05% Ti is an element added to fix N and ensure the improvement of hardenability by adding B. To obtain such an effect, Ti is added in an amount of 0.1 to 0.05%. It is necessary that the content be 01% or more. However, if the content is too large, the toughness is reduced. Therefore, the content is limited to 0.05% or less.

S: 0.01 to 0.10%, Pb: 0.0
1 to 0.20%, Bi: 0.01 to 0.30%, Te:
0.005 to 0.10%, Ca: 0.0003 to 0.0
10% or more S, Pb, Bi, Te, and Ca are effective elements for improving machinability, and may be appropriately added in the above range as needed.

Hardened layer depth and shot peening condition: If the hardened layer ratio is less than 0.5, the effect of residual stress by shot peening is sufficient because the fracture originating point is a cracked area as shown in FIG. Since it cannot be obtained, the cured layer ratio needs to be 0.5 or more. Furthermore, the fatigue strength is improved by increasing the compressive residual stress of the surface layer by performing shot peening, but in this case, if the shot grain size exceeds 1.5 mm, the surface of the member becomes rough and the fatigue strength is reduced. Therefore, the shot particle size needs to be 1.5 mm or less. On the other hand, if the shot grain hardness is lower than 650 HV, a sufficient residual stress cannot be provided, and
If it exceeds HV, the surface is roughened and the fatigue strength is reduced. Therefore, it is necessary to use a shot material of 600 to 850 HV. Further, when the shot peening strength is compared with the arc height when the most commonly used Almen strip A is used, when the arc height value is low, a sufficient residual stress cannot be applied, and when the arc height value is high, the component is not high. Since the surface is rough and the fatigue strength is reduced, the shot particle size is 0.5 to
For 1.5 mm, the shot diameter needs to be 0.5 to 1.2 mmA, and for the shot particle diameter of 0.03 to 0.5 mm, it needs to be 0.15 to 0.50 mmA.

[0018]

EXAMPLES The effects of the present invention will be described with reference to examples. After smelting steel having the chemical composition shown in Table 1, a bar having a diameter of 40 mm was formed by hot forging. After normalizing, the outer diameter of the parallel portion was 22 m.
m, a torsion fatigue test piece having a parallel portion inner diameter of 8 mm and a lateral hole of 4 mm was further processed. Thereafter, induction hardening was performed under the conditions shown in Table 2, and shot peening was performed under the conditions shown in Table 3. At this time, the hardness distribution of the cross section of the test piece was measured, and the surface hardness and the depth of the hardened layer were examined. Here, the depth up to 50% martensite hardness was defined as the hardened layer depth. In the torsional fatigue test, a sine wave torque of 2 Hz was applied, and the torque value at the number of times of repeated breaking of 3 × 10 ⁵ was defined as the torsional fatigue strength. Table 4 shows the results.

As is evident from Table 4, all the samples according to the method of the present invention exhibit excellent torsional fatigue strength. On the other hand, Comparative Examples 3, 14, 21, 24, 42, and 49 satisfy the component range of the present invention, but the induction hardening is a shallow quenching treatment, so that the depth of the hardened layer is small, and furthermore, shot peening is performed. Is not high enough to obtain sufficient torsional fatigue strength. Furthermore, in Comparative Examples 1, 4, 45, 50, 52, and 56, the arc height value of shot peening was sufficient, but the effect of shot peening was not obtained because the depth of the hardened layer was small, and the torsional fatigue strength was low. I have. Comparative Examples 58, 59 and 60 are C
Since the content and the Mn content are low, the hardened layer ratio is smaller than 0.5 even under the condition of deep quenching by induction hardening, and the torsional fatigue strength is low. In Comparative Examples 61 and 62, the depth of the hardened layer was sufficient, but the C content was large, so that the test pieces were cracked. Next, in Comparative Examples 6, 9, 34, and 39, the depth of the hardened layer satisfies the range of the present invention, but sufficient strength was not obtained because shot peening was not performed. Comparative Example 10,
In Nos. 15, 27, 35 and 47, the depth of the hardened layer is sufficient and the shot peening treatment is performed. However, since the arc height value is low, a sufficient effect of the shot peening cannot be obtained and the fatigue strength is low.

[0020]

[Table 1]

[0021]

[Table 2]

[0022]

[Table 3]

[0023]

[Table 4]

[0024]

[Table 5]

[0025]

As is clear from the above description, in the present invention, it is possible to improve the fatigue strength of a shaft part having a machine structure having a lateral hole by applying induction hardening and shot peening. .

[Brief description of the drawings]

FIG. 1 is a perspective view of a shaft member.

FIG. 2 is a longitudinal sectional view of a shaft member.

FIG. 3 is an enlarged schematic diagram showing a hardened layer and a non-hardened layer around a lateral hole after induction hardening of a shaft member.

FIG. 4A is a simulated view showing a damage starting point when a hardened layer is shallow. (B) is a mimetic diagram showing a fracture starting point when a hardened layer is deep.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI C22C 38/00 301 C22C 38/00 301Y 38/18 38/18 38/60 38/60 (72) Inventor Yutaka Kobayashi Handa, Aichi 5-2-17-1 Miyamoto-cho, Ichigo (72) The inventor Sadayuki Nakamura 3094 Kaki, Asahimachi, Mie-gun, Mie Prefecture

Claims (4)

[Claims] C .: 0.25 to 0.55 by weight%
%, Si: 0.30% or less, Mn: 0.20 to 1.50
%, Cr: 0.05-1.30%, Al: 0.01-
When manufacturing shaft-shaped parts for machine structures using induction hardened steel containing 0.06%, the hardened layer ratio of the hole perpendicular to the axial direction is t / R = 0.5 or more (t: 5
In the case of a hardened layer depth up to 0% martensite hardness, R: component radius) or a hollow product, t / T = 0.5 or more (T:
After performing an induction hardening on the wall thickness) and further performing a shot peening process on the side hole portion with an arc height of 0.5 to 1.2 mmA using a shot material having a particle size of 0.5 to 1.5 mm and a hardness of 600 to 850 HV. , Particle size 0.03-0.5mm,
A shot material with a hardness of 600 to 850 HV is arc height 0.1
A method for producing a shaft-shaped part for a machine structure by performing a shot peening process of 5 to 0.50 mmA or performing a shot peening process independently. 2. In addition to the alloy component according to claim 1,
B: 0.0005-0.0035%, N: 0.015%
Hereinafter, a method for producing a shaft part for a machine structure, characterized by using a steel for induction hardening containing 0.01 to 0.05% of Ti. 3. A steel for induction hardening containing one or two of Mo: 0.5% or less and Ni: 1.0% or less in addition to the alloy components according to claim 1 or 2. An axial part for a machine structure, characterized by using: 4. The method according to claim 1, 2 or 3.
In addition to the alloy components described in the above, S: 0.01 to
0.10%, Pb: 0.01 to 0.20%, Bi:
0.01 to 0.30%, Te: 0.005 to 0.10
%, Ca: one or two of 0.0003 to 0.010%
A method for producing a shaft-shaped part for a machine structure, characterized by using induction hardening steel containing at least one kind.